Clean Up Behind You ‐ Novel Patterning Approach for Solid Immersion Lenses

ABSTRACT Solid‐state immersion lenses have the potential to become a key component in photonic quantum technologies, as they enable efficient collection of quantum light. Although they are conceptually simple and powerful at the same time, they are not yet widely used today. This is a consequence of the challenges in the controlled processing of the typically ultra‐hard crystalline materials such as diamond in combination with the deterministic positioning of the lens relative to the position of the quantum emitter. Here we present a novel patterning approach for the fabrication of solid‐state immersion lenses using focused ion beam milling, which eliminates the need for post‐processing. The hemispherical lens shape is defined by a radially varying ion flux applied in a continuous Archimedean spiral beam path. In line with the prediction from continuum modeling, we observe periodic surface corrugations at the side walls of the lenses indicating that the ion flux is locally perfectly homogenized by our approach. Microstructural investigations reveal a damage layer of only 10 – 15 nm above an otherwise intact diamond crystal. This corresponds to the expected beam damage obtained from atomistic binary collision modeling, and proves that redeposition is indeed negligible. To demonstrate their performance, lenses with nitrogen vacancy centers are optically examined, revealing a sixfold enhancement in light collection efficiency in combination with reduced background noise.